to get the difference in seconds and then calculate it out to get your answer in days,hours,min,seconds.

Look for a script called "scriptomatic". Its an amazing piece of work that shows examples of how to use WMI in autoit while showing the results from querying your own machine.

Hopefully this points you in the right direction. When I discovered WMI objects I suddenly had a means to get amost any info I needed from network machines. Check them out. Scriptomatic helped me alot in figuring out how to interact with them.